Ionization is one of the key components in controlling an electrostatic environment. Typical electronic components are manufactured using a plurality of processes. With the increasing sensitivity of electronic components (due to the smaller and smaller sizes of the features in those electronic components), the process' performance with respect to controlling ionization is under increased scrutiny to improve and to control their performance. An improperly functioning ionizer may actually charge sensitive components instead of discharging them. At best, poorly-functioning ionizers offer a false sense of security which is not acceptable in volume production of static-sensitive components, such as semiconductors, disk drive magnetic head, flat panel displays, etc.
Several methods exist currently that offer limited control over ionization. One method involves periodic tests using a charge plate monitor. This method does measure the ionization during the test, but does not offer any assurance of proper ionization in between the tests. In addition, such tests are often performed in the places where sensitive components are not handled so that the test is not measuring ionization at the appropriate place in the processes. These periodic tests are also time-consuming and require dedicated trained personnel to perform the tests. Another method involves built-in ionizer feedback controls. An example of such a control is a metal grill placed in front of an ionizer blower, such as Ion Systems' 5810 and Simco Centurion models. The grill functions as a sensor of ionizer balance and, using an internal control circuit of an ionizer, can automatically adjust balance within certain limits. The problem with this approach is that it offers only limited benefits. There is no guarantee that the balance in the immediate proximity to the ionization tips is the same as the balance away from the ionizer at the target of ionization. For example, the humidity of the air may significantly offset the resulting balance of ionization at the benchtop while it may be acceptable in the immediate proximity to the ionizer at the location of the grill. Zero balance may also mean that the decay function of an ionizer is not working.
Another prior system uses remote sensors with feedback to the ionizer to control the balance. Examples of the prior system include the EM Aware monitor CTC034-031-F by Credence Technologies and 5315 monitor by Novx. These monitors are capable of adjusting the balance of specially-equipped ionizers (such as Ion Systems' 5810 and Simco'Centurion models) according to the actual balance at the point of measurement. There are several deficiencies of this method. First, there is an inherent delay between the application of a control signal and the change of voltage at the point of control due mostly, but not exclusively, to the airflow from the ionizer to the workplace. Such delay makes tight control over balance nearly impossible. Aggravating the situation is that charged objects that may approach the sensor in normal production environment create a similar signal as from an imbalanced ionizer which causes the controller to send the ionizer a false correction signal that may cause severe imbalance charging at the target area to voltages as high as 100V or more. To alleviate this situation, manufacturers introduce delay and integration into the control circuit, however this makes real-time control of ionization balance impossible. Although sensors that offer monitoring of decay of ionization exist (such as above-mentioned EM Aware ESD monitor), no device and system currently exists to correct the performance of an ionizer based on decay performance information at the target point. In addition, there is no method that exists to control ionization from pulsed ionizers, such as Ion Systems' 5285 and others.
Thus, it is desirable to provide a method and device for controlling ionization that corrects these and other deficiencies with typical system and offers complete control over ionization parameters and it is to this end that the present invention is directed.